RO/DI questions

I just got a used seachem ro/di unit. The unit was not used for about 8 months. I figured that I would need new membranes and filters. I kicked it on today just to see if my TDS meter works. And my meter was reading 350 ro and between 3 and 4 at the out put. Is 3 or 4 ok? Should I even use these membranes?

 

The readings you are getting on the TDS are fine , I like to change my filters at 10, if you have not changed the filters yet I would not chance anything as you don't know what was put through the filter. Goodluck.

 

Most people like to change the DI when the TDS gets between 5-15 ppm. You said your RO TDS reading was 350? Did you mean before the membrane it was 350 and 3-4 coming after the membrane?

 

350 after going through the ro and 3-4 coming out of the di

 

Ok. What's the TDS of your tap? It sounds like you will need a new membrane soon. The membrane is supposed to be lessening the work of the DI. At 350 ppm going into the DI, the DI will exhaust quickly.

Here is a link to a membrane webpage for Air, Water & Ice, Inc. Take a look if you want to.
www.airwaterice.com FilmTec Membrane 75 GPD

 

I went and looked at the TDS again. Its coming out of the tap at 350, coming out of the RO at 45, and out of the di at 3.

 

Ok. Your membrane is rejecting only about 87.5% of the TDS. For a RO/DI unit, you would want your membrane to be rejecting between 95%-99% at least. This lessens the work of the DI and extends its life giving you better quality water (-0- TDS water). Anything below 95% is causing your DI to work 2-3 times harder to remove the excess TDS.

 

What he said! lol!